Current teleconferencing systems cannot easily facilitate private conversations among teleconference participants who wish to communicate with each other (or with third parties) during a teleconference without being overheard by the remaining teleconference participants but while still being able to monitor the teleconference. In conventional teleconferencing systems, a teleconference participant desiring to collaborate with another teleconference participant or third party (the "collaborator") would be required to place the teleconference on "hold" and place a second call to the collaborator. However, there would no means for the first conferee to continue to monitor the teleconference while communicating with the collaborator. Of course, direct communication with the collaborator on the teleconference line is not feasible since that would disrupt the teleconference.
In Eppe U.S. Pat. No. 5,034,947, there is described a "whisper circuit" for a conference call that permits two parties in a conference call to conduct a whisper conference between each other without being heard by the other parties on the conference call. At the same time, the two parties to the whisper conference can still hear the entire conversation being carried on by all of the other parties to the conference call, without the other parties being aware that the two parties are engaged in a whisper conference. Teleconference participants are interconnected to a digitized conference bridge over PCM telephone carrier lines, which are connected to a cross-point switch for interchanging the PCM speech data occurring in time slots for the two whisper conferees so that the PCM speech data for the first of the two whisper conferees is placed in the time slot for the second of the two whisper conferees and vice versa. A summation circuit is utilized to sum the telephone conversations of all remaining conferees and the two interchanged telephone conversations of the whisper conferees are then selectively added to the summed signals. Intelligibility is hampered somewhat because there is no acoustic isolation of the whisper conference. This is because a whisper conferee must extract the collaborator's voice out of the summed signals. This prior art teleconferencing circuit, which requires special system based hardware and resources, does not allow a teleconference participant to initiate a whisper conference with a third party who is not a member of the teleconference.
It is beneficial to allow for whisper conferencing (or collaborative conferencing) without the need for the teleconference bridge and digital signalling processing techniques set out in this prior art patent which are typically difficult and expensive to implement. Furthermore, since a conference bridge is a shared resource concentrated at the network, there is an upper limit on the number of teleconferences that can be accommodated with whisper circuit functionality. The whisper circuit of the prior art patent will not function unless a digital voice switch hosts the teleconferencing bridge that is essential to the operation of that invention. Finally, the whisper circuit of the prior art patent restricts the number of whisper conferees to two since multiple collaborations cannot be accommodated.